﻿#region

using System;

#endregion

namespace terrain
{
    public class Noise
    {
        // simplex noise in 2D, 3D and 4D
        private readonly int[][] grad3 =
        {
            new[] {1, 1, 0}, new[] {-1, 1, 0}, new[] {1, -1, 0}, new[] {-1, -1, 0},
            new[] {1, 0, 1}, new[] {-1, 0, 1}, new[] {1, 0, -1}, new[] {-1, 0, -1},
            new[] {0, 1, 1}, new[] {0, -1, 1}, new[] {0, 1, -1}, new[] {0, -1, -1}
        };

        private readonly int[] p =
        {
            151, 160, 137, 91, 90, 15,
            131, 13, 201, 95, 96, 53, 194, 233, 7, 225, 140, 36, 103, 30, 69, 142, 8, 99, 37, 240, 21, 10, 23,
            190, 6, 148, 247, 120, 234, 75, 0, 26, 197, 62, 94, 252, 219, 203, 117, 35, 11, 32, 57, 177, 33,
            88, 237, 149, 56, 87, 174, 20, 125, 136, 171, 168, 68, 175, 74, 165, 71, 134, 139, 48, 27, 166,
            77, 146, 158, 231, 83, 111, 229, 122, 60, 211, 133, 230, 220, 105, 92, 41, 55, 46, 245, 40, 244,
            102, 143, 54, 65, 25, 63, 161, 1, 216, 80, 73, 209, 76, 132, 187, 208, 89, 18, 169, 200, 196,
            135, 130, 116, 188, 159, 86, 164, 100, 109, 198, 173, 186, 3, 64, 52, 217, 226, 250, 124, 123,
            5, 202, 38, 147, 118, 126, 255, 82, 85, 212, 207, 206, 59, 227, 47, 16, 58, 17, 182, 189, 28, 42,
            223, 183, 170, 213, 119, 248, 152, 2, 44, 154, 163, 70, 221, 153, 101, 155, 167, 43, 172, 9,
            129, 22, 39, 253, 19, 98, 108, 110, 79, 113, 224, 232, 178, 185, 112, 104, 218, 246, 97, 228,
            251, 34, 242, 193, 238, 210, 144, 12, 191, 179, 162, 241, 81, 51, 145, 235, 249, 14, 239, 107,
            49, 192, 214, 31, 181, 199, 106, 157, 184, 84, 204, 176, 115, 121, 50, 45, 127, 4, 150, 254,
            138, 236, 205, 93, 222, 114, 67, 29, 24, 72, 243, 141, 128, 195, 78, 66, 215, 61, 156, 180
        };

        // To remove the need for index wrapping, double the permutation table length
        private readonly int[] perm = new int[512];

        public Noise(int seed)
        {
            Random rand = new Random(seed);
            for (int i = 0; i < p.Length; i++)
                p[i] = (byte)rand.Next();
            for (int i = 0; i < 512; i++)
                perm[i] = p[i & 255];
        }

        // This method is a *lot* faster than using (int)Math.floor(x)
        private int fastfloor(double x)
        {
            return x > 0 ? (int)x : (int)x - 1;
        }

        private double dot(int[] g, double x, double y, double z)
        {
            return g[0] * x + g[1] * y + g[2] * z;
        }

        public float GetNoise(double pX, double pY, double pZ)
        {
            double n0, n1, n2, n3; // Noise contributions from the four corners
            // Skew the input space to determine which simplex cell we're in
            double F3 = 1.0 / 3.0;
            double s = (pX + pY + pZ) * F3; // Very nice and simple skew factor for 3D
            int i = fastfloor(pX + s);
            int j = fastfloor(pY + s);
            int k = fastfloor(pZ + s);
            double G3 = 1.0 / 6.0; // Very nice and simple unskew factor, too
            double t = (i + j + k) * G3;
            double X0 = i - t; // Unskew the cell origin back to (x,y,z) space
            double Y0 = j - t;
            double Z0 = k - t;
            double x0 = pX - X0; // The x,y,z distances from the cell origin
            double y0 = pY - Y0;
            double z0 = pZ - Z0;
            // For the 3D case, the simplex shape is a slightly irregular tetrahedron.
            // Determine which simplex we are in.
            int i1, j1, k1; // Offsets for second corner of simplex in (i,j,k) coords
            int i2, j2, k2; // Offsets for third corner of simplex in (i,j,k) coords
            if (x0 >= y0)
            {
                if (y0 >= z0)
                {
                    i1 = 1;
                    j1 = 0;
                    k1 = 0;
                    i2 = 1;
                    j2 = 1;
                    k2 = 0;
                } // X Y Z order
                else if (x0 >= z0)
                {
                    i1 = 1;
                    j1 = 0;
                    k1 = 0;
                    i2 = 1;
                    j2 = 0;
                    k2 = 1;
                } // X Z Y order
                else
                {
                    i1 = 0;
                    j1 = 0;
                    k1 = 1;
                    i2 = 1;
                    j2 = 0;
                    k2 = 1;
                } // Z X Y order
            }
            else
            {
                // x0<y0
                if (y0 < z0)
                {
                    i1 = 0;
                    j1 = 0;
                    k1 = 1;
                    i2 = 0;
                    j2 = 1;
                    k2 = 1;
                } // Z Y X order
                else if (x0 < z0)
                {
                    i1 = 0;
                    j1 = 1;
                    k1 = 0;
                    i2 = 0;
                    j2 = 1;
                    k2 = 1;
                } // Y Z X order
                else
                {
                    i1 = 0;
                    j1 = 1;
                    k1 = 0;
                    i2 = 1;
                    j2 = 1;
                    k2 = 0;
                } // Y X Z order
            }
            // A step of (1,0,0) in (i,j,k) means a step of (1-c,-c,-c) in (x,y,z),
            // a step of (0,1,0) in (i,j,k) means a step of (-c,1-c,-c) in (x,y,z), and
            // a step of (0,0,1) in (i,j,k) means a step of (-c,-c,1-c) in (x,y,z), where
            // c = 1/6.

            double x1 = x0 - i1 + G3; // Offsets for second corner in (x,y,z) coords
            double y1 = y0 - j1 + G3;
            double z1 = z0 - k1 + G3;
            double x2 = x0 - i2 + 2.0 * G3; // Offsets for third corner in (x,y,z) coords
            double y2 = y0 - j2 + 2.0 * G3;
            double z2 = z0 - k2 + 2.0 * G3;
            double x3 = x0 - 1.0 + 3.0 * G3; // Offsets for last corner in (x,y,z) coords
            double y3 = y0 - 1.0 + 3.0 * G3;
            double z3 = z0 - 1.0 + 3.0 * G3;
            // Work out the hashed gradient indices of the four simplex corners
            int ii = i & 255;
            int jj = j & 255;
            int kk = k & 255;
            int gi0 = perm[ii + perm[jj + perm[kk]]] % 12;
            int gi1 = perm[ii + i1 + perm[jj + j1 + perm[kk + k1]]] % 12;
            int gi2 = perm[ii + i2 + perm[jj + j2 + perm[kk + k2]]] % 12;
            int gi3 = perm[ii + 1 + perm[jj + 1 + perm[kk + 1]]] % 12;
            // Calculate the contribution from the four corners
            double t0 = 0.6 - x0 * x0 - y0 * y0 - z0 * z0;
            if (t0 < 0)
                n0 = 0.0;
            else
            {
                t0 *= t0;
                n0 = t0 * t0 * dot(grad3[gi0], x0, y0, z0);
            }
            double t1 = 0.6 - x1 * x1 - y1 * y1 - z1 * z1;
            if (t1 < 0)
                n1 = 0.0;
            else
            {
                t1 *= t1;
                n1 = t1 * t1 * dot(grad3[gi1], x1, y1, z1);
            }
            double t2 = 0.6 - x2 * x2 - y2 * y2 - z2 * z2;
            if (t2 < 0)
                n2 = 0.0;
            else
            {
                t2 *= t2;
                n2 = t2 * t2 * dot(grad3[gi2], x2, y2, z2);
            }
            double t3 = 0.6 - x3 * x3 - y3 * y3 - z3 * z3;
            if (t3 < 0)
                n3 = 0.0;
            else
            {
                t3 *= t3;
                n3 = t3 * t3 * dot(grad3[gi3], x3, y3, z3);
            }
            // Add contributions from each corner to get the final noise value.
            // The result is scaled to stay just inside [-1, 1] - now [0, 1]
            return (32.0f * (float)(n0 + n1 + n2 + n3) + 1) * 0.5f;
        }
    }
}